Accuracy of Metering Pump and Way of Adjusting Mechanism

Most people maybe heard about the actual use of the metering pump, but do you know that you should pay attention to the accuracy problem when using it?

Ⅰ. Three accuracy problems should be paid attention to when using metering pump

1. Steady state accuracy of metering pump

The rated flow is ± 2%. If the measured 100% stroke flow of the metering pump is 1000L / h, the allowable deviation of steady-state accuracy is ± 2% * 1000 = ± 20L / h. Steady state accuracy refers to the flow deviation obtained by calibrating the flow of the dosing pump at different time points without any adjustment and change.

2. Linear accuracy of metering pump

The rated flow is ± 3%. If the measured 100% stroke flow of the metering pump is 1000L / h, the allowable deviation of linear accuracy is ± 3% * 1000 = ± 30L / h. The linear accuracy refers to the deviation between the measured flow and the fitting value obtained by uniformly selecting different stroke points for flow calibration within the stroke range of 10% ~ 100% of the metering pump.

3. Repetition accuracy of metering pump

The rated flow is ± 3%. If the measured 100% stroke flow of the dosing metering pump is 1000L / h, the allowable deviation of repetition accuracy is ± 3% * 1000 = ± 30L / h. Repetition accuracy refers to the resulting flow deviation. Within the range of 10% ~ 100% stroke of the metering pump, select a stroke point for flow calibration, and then change the stroke of the pump. After a period of time, return to the original stroke point for flow calibration.

Ⅱ. Use and mode of metering pump regulating mechanism

In order to change the flow of the metering pump in the conveying process, different adjustment methods can be adopted.

1. Adjust the stroke length.

2. Adjusting speed includes adjusting speed and adjusting stroke speed.

3. Adjust the stroke length and speed.

Although various adjustment methods are listed above, the most common method is to change the stroke length and speed. Among them, the speed regulation is mostly used in the metering pump group of combined multi connection structure. The metering pump set is a plurality of single metering systems driven by one motor. By changing the number of revolutions to control the flow of the pump device, the flow ratio between each device remains unchanged.

The flow regulation of each unit can be realized by changing their respective stroke length, so as to change the mixing ratio. However, the method of adjusting the number of revolutions alone is rarely used because it requires expensive transmission mechanism and huge structure. More importantly, when the motor speed is low, the time interval between suction and discharge is too long, which affects the discharge flow.

In fact, adjusting the stroke length is the most commonly used method. The method is simple and feasible, and can still meet the linear requirements under small flow. There are two adjustment modes: manual knob adjustment; The electric stroke regulating device is installed and connected with the customer SCADA system to adjust the stroke length through remote 4-20mA current signal or RS485 communication signal, so as to achieve the purpose of real-time control of metering pump flow.